Nachi variant wipes MyDoom from PCs

Virus War gets really confusing

A new variant of the Nachi worm which attempts to cleanse computers infected by MyDoom and download Microsoft security patches to unprotected computers has careened onto the Net this morning.

Nachi-B (AKA Welchi) uses the same security vulnerability exploited by the Blaster worm to spread. Once it infects target machines the worm attempts to search and destroy any traces of MyDoom infection - before downloading patches for the Microsoft vulnerability it used to infect the system in the first place.

The worm might display a text saying "LET HISTORY TELL FUTURE !" and make references to the dropping of atomic bombs during WWII, according to a preliminary analysis by F-Secure.

The original Nachi worm, seen in August 2003, attempted to remove infections from computers infected by Blaster.

The scanning traffic generated by the original Nachi worm caused huge problems. AV vendors fear a repeat performance this time around. This concern is compounded by the plethora of new viruses released in recent days. As well as the Doomjuice worms (which target Microsoft's Web site in DDoS attacks), we have MyDoom and variants and now a Nachi variant.

As if that little lot wasn't enough, today also saw the arrival of a Trojan, called Mitglieder-H, with the ability to spread to computers infected with the MyDoom-A worm.

One small comfort is that MyDoom-A, the biggest menace, stops spreading today.

The Microsoft security patch to defend against the vulnerability exploited by the Nachi and Blaster can be found here. To scan Windows boxes for security vulnerabilities visit Windows Update here. ®